Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Patent
1985-01-10
1987-05-26
Kittle, John E.
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
222591, 222603, B22D 4702, B22D 2710, B22D 3700
Patent
active
046685545
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the manufacture of refractory products used for handling and conveying molten metals. Thus this invention is particularly concerned with nozzles, ladle to tundish shrouds, valves, blocks, stoppers and crucibles. All these find a use in melting, containing or pouring of molten steel in steel works, steel foundries and iron foundries but especially in continuous casting operations. There are also applications for refractory products in the melting, containing or pouring and forming of non-ferrous metals such as copper based alloys and aluminium.
The refractory materials used for this purpose generally comprise graphite, alumina and silica or silicon carbide with small quantities of special purpose additives. Depending on the method used to form a product from these materials, the product may be permeable or non-permeable. Similarly the type of additives included in the product affect such properties as electrical resistivity, resistance to erosion and corrosion by the melt and slag and thermal shock resistance.
One method which has been found to be particularly effective in producing such products is that involving isostatic pressing of a fine particulate refractory material in a mould to shape the product.
An object of the present invention is to provide an improvement in this method whereby more control over the properties of the finished product is obtained and thereby provide an improved product capable of many specialised applications.
According to the present invention there is provided a composite refractory product for use in the handling of molten metal comprising a body of refractory material having therein or thereon a flexible gas-impermeable membrane formed from a compatible refractory material to render at least a portion of said body impermeable to gas.
The term "refractory material" as used herein means a material capable of withstanding the conditions normally found in molten metal handling when used in the manner described herein and includes silica, silicon carbide, alumina, graphite/alumina, zirconia, magnesite, boron or silicon nitride and graphite or carbon/graphite mixtures.
The term "compatible refractory material" means a refractory material which in comparison with another refractory material required to form the intended refractory product is sufficiently similar thereto in chemical and physical properties as to allow isostatic pressing to form a usable product and thereafter withstand the conditions of use without degradation of the product. In view of the intended use of such a product, the only property which requires careful consideration is the thermal expansion coefficient and it is expected that a wide range of refractory materials may be combined to form a product for the purposes outlined herein. For example where the product is to be made primarily from alumina, a flexible membrane made from alumina would be preferred. Boron or silicon nitrides are also suitable but more expensive. Flexible graphite which has been found to be effective for the purposes of this invention is commercially available and information on manufacture thereof can be found in U.S. Pat. No. 3,404,061.
The membrane can be made from known flexible graphite sheets or tape but can alternatively be made from carbon/graphite produced, for example, from carbon fibres, or from similar fibres.
Further according to this invention there is provided a method of manufacturing the composite refractory product which comprises providing within an isostatic pressing mould a flexible gas-impermeable membrane and particulate refractory materials, the said membrane being formed from a refractory material which is compatible with the particulate refractory materials and being suspended or supported in the mould such that after packing of the particulate refractory materials in the mould and subjecting the mould to isostatic pressing a refractory body having the said flexible membrane in or on the said body at a predetermined position is produced.
Preferably the flexible gas-impermeable membrane
REFERENCES:
patent: 3404061 (1968-10-01), Shane et al.
patent: 3435992 (1969-04-01), Tisdale et al.
patent: 3475244 (1969-10-01), Sanders, Jr.
patent: 3499066 (1970-03-01), Murray
patent: 4108339 (1978-08-01), Lunde
Ferguson Jr. Gerald J.
Hoffman Michael P.
Kittle John E.
Malamud Ronni S.
Thor Ceramics Limited
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